A tank system of a commercial aircraft comprises a plurality of tank cells, which are conventionally disposed in the wings and in the middle wing box of the aircraft. Filling the tank system with fuel may be effected centrally by pressure refueling through a tank filler neck disposed in the region of a wing. Alternatively, refueling through a plurality of decentralized tank filler necks is also possible. During a refueling operation air displaced from the tank system is conveyed through ventilation lines to ventilation stubs provided in the region of the wing tips and is discharged from there into the environment. The air escaping from the tank system contains fuel vapour, wherein the fuel quantity that evaporates during the refueling operation depends upon the actual fuel saturation of the air, the temperature, the pressure and the nature of the fuel.
When refueling an aircraft with conventional kerosene, at an ambient temperature of 20° C. 11.9 ml/m3 evaporates, substantially in the form of pentadecane. This means that, for example at Frankfurt airport where on peak days 18 million litres of kerosene are used to refuel aircraft, 214.1 litres of kerosene per day escape into the environment. The evaporation of fuel during aircraft refueling leads to a not inconsiderable loss of fuel that, given higher ambient temperatures and/or the use of more highly volatile alternative fuels, may even markedly exceed the values mentioned above. For example, it is reckoned that the use of ethanol fuel instead of kerosene would lead at Frankfurt airport to a fuel vapour emission of 790 t per year. Besides the economic loss, fuel vapour emission poses risks to safety and moreover has a negative impact on the environment. For these reasons, for some time now efforts have been directed towards preventing or at least minimizing the emission of fuel vapour during the refueling of aircraft.
U.S. Pat. No. 2,965,196 and U.S. Pat. No. 5,782,258 describe in each case an adsorption device that is connectable to a ventilation stub of a tank. The adsorption device contains an adsorbent material, such as for example fine-grained activated carbon, for adsorbing hydrocarbons that leave the tank during the refueling operation. These known systems have the drawback that the fuel attached to the adsorbent material is either impossible to recover or may be recovered only with a relatively high equipment outlay. The systems of prior art are therefore not suitable for use on board an aircraft.
The underlying object of the invention is to provide an aircraft tank system and a refueling unit for refueling an aircraft tank system that in a simple manner and while taking up a minimum of additional installation space prevent the emission of fuel vapour into the environment during a refueling operation and enable a recovery of the evaporated fuel. A further underlying object of the invention is to indicate a method of refueling an aircraft that is easy to carry out, prevents the emission of fuel vapour into the environment and enables a recovery of the fuel that has evaporated during the refueling operation.